Effect of friction at the supports of semi-circular bending tests on fracture mode of loading

This paper aims to provide an investigation of the impact of supports on fracture mode of loading using semicircular bending (SCB) specimen. A crack with an angle of a is assumed within the SCB specimen, and extensive finite element analyses are performed by altering some important parameters namely crack angle, crack length, span and friction coefficient at the supports. According to the numerical results, all these parameters can influence the values of geometry factors Y-I and Y-II. Interestingly, it is found that the friction coefficient (or support type) can significantly change the mode of loading at the crack tip. To verify this issue, some experiments on a rock material are also carried out under different fracture modes using three various types of supports called type I, type II and type III. Based on the results of finite element and tests, in order to produce the same mode of loading using the mentioned support types, the crack angle should be changed. In other words, the crack angles of 29, 25 and 23 degrees should be respectively used for the support types of I, II and III to produce the same mixed mode of loading with M-e = 0.5. Likewise, they should be regarded as 41, 37 and 36 degrees for the support types of I, II and III to produce the pure mode II loading. Furthermore, the friction coefficients for the mentioned support types are computed.